. "Rafts are a way of '''concentrating receptors, the lipids and lipid tethered proteins''' together to provide the elements needed to activate secondary signals. (http://bioweb.wku.edu/courses/biol566/L19SignalPathnonRPTK.html) * On lipid rafts: Plasma membranes are heterogeneous and contain microdomains for lipid composition and receptors, especially in T and B lymphocytes and mast cells." . . .